The present invention relates to 2,5-dimercapto-1,3,4-thiadizaole dimer reaction products and adducts useful as extreme pressure additives, and more particularly to 2,5-dimercapto-1,3,4-thiadiazole dimer/glycol reaction products and adducts useful as extreme pressure additives.
A variety of additives are used in lubricants to substantially improve performance. For example, extreme pressure additives are routinely incorporated into an untreated lubricating composition (e.g., greases) to significantly improve performance. Extreme pressure additives are believed to produce a film on the surface of a metal which can both increase the load carrying capacity of lubricant, and protects the metal surface under high load conditions from deterioration due to wear, welding, and abrasion.
Lead naphthenates and lead dialkyldithiocarbamates are frequently used as additives to improve the EP performance of greases. However, lead is a heavy metal which is considered xe2x80x9cpoisonousxe2x80x9d in all forms. As an alternative, metal additives (such as antimony, zinc, and bismuth) have been used as a replacement for lead. However, these heavy metals still provide environmental concerns regarding the use. Accordingly, it has long been a goal in the art to develop non-metal lubricating materials to replace heavy metal additives while providing acceptable extreme pressure performance.
The effectiveness of potential extreme pressure additives is conventionally ascertained by the 4-Ball Weld Test (ASTM D-2596) and the Timken Load Test (ASTM D-2509). An ideal candidate compound should exhibit good results in both tests since each test quantitates different extreme pressure properties.
Known to those skilled in the art 2,5-dimercapto-1,3,4-thiadiazole (DMTD) derivatives are effective as anti-wear additives in lubricants. Examples of DMTD derivatives useful as anti-wear additives include the monosulfide and disulfide dimers of DMTD as disclosed in U.S. Pat. Nos. 4,517,103 and 5,194,621, maleate adducts of DMTD as disclosed in U.S. Pat. Nos. 5,102,568, 5,055,584 and 5,138,065 and mono-alkylated and thioacteal derivatives as disclosed in U.S. Pat. No. 5,849,925.
DMTD derivatives are also known to provide good 4-Ball Weld properties. In fact, the 4-Ball Weld properties of DMTD derivatives often exceed commercial requirements. Unfortunately, these same derivatives generally exhibit poor Timken Load performance since the DMTD derivatives do not generally provide Timken Loads levels greater than 35 pounds. As a result, commercialization of DMTD derivatives as extreme pressure additives has been limited.
In view of the above, there exists a need in the art for DMTD derivative that provide both adequate 4-Ball Weld and Timken Load properties. Accordingly, it is an object of the present invention to provide DMTD derivatives that provide adequate 4-Ball Weld and Timken Load properties, which will allow for the effective utilization of DMTD derivatives as extreme pressure additives.
The present invention provides 2,5-dimercapto-1,3,4-thiadiazole dimer/glycol reaction products and adducts useful as extreme pressure additives. In one embodiment, an additive is provided including the reaction product of: 
where Z is hydrogen, an alkyloxy linkage having formula (II): 
where F is a hydroxyl radical, a branched or straight chain C1 to C20 alkoxyl radical, a branched or straight chain C1 to C20 alkylcarboxyl radical, a mono-substituted, di-substituted, or tri-substituted glycerol residue, hydrogen, or combinations thereof; where R3 is hydrogen, a methyl radical, or combinations thereof; where R4 is hydrogen, a branched or straight chain C1 to C20 alkyl radical, a phenyl radical, a C1 to C8 branched or straight chain alkyl-substituted-phenyl radical, a C1 to C20 branched or straight chain acyl radical, or combinations thereof; and with q being 1 to 300.
In another embodiment, an additive is provided including mono-substituted and di-substituted thiadiazole condensation adducts having formulas (IV) and (V), respectively: 
in which R1, R3 and R4 are independently selected from the above-described group of substituents for the reaction products and n is 1 to 2. The number of repeating ether units xe2x80x9cmxe2x80x9d in the glycol moiety is 1 to 50.
In another embodiment, an additive is provided including the reaction product of: (A) a thiadiazole dimer having formula (VI): 
where d is 1 to 5 and Z is hydrogen, an alkyloxy linkage having formula (II): 
or combinations thereof, with R1 being hydrogen, a branched or straight chain C1 to C7 alkyl radical, or combinations thereof and R2 being hydrogen, a branched or straight chain C1 to C7 alkyl radical, or combinations thereof, wherein t is 0 or 1; and
(B) a poly(ether)glycol having formula (III): 
In an alternative embodiment, an additive is provided including the reaction product of:
(A) a thiadiazole compound being 
or combinations thereof, where Z is hydrogen, an alkyloxy linkage having formula (II): 
or combinations thereof, with R1 being hydrogen, a branched or straight chain C1 to C7 alkyl radical, or combinations thereof and R2 being hydrogen, a branched or straight chain C1 to C7 alkyl radical, or combinations thereof, where n is 1 to 2 and t is 0 or 1; and
(B) a poly(ether)glycol having formula (III): 
where F is a hydroxyl radical, a branched or straight chain C1 to C20 alkoxyl radical, a branched or straight chain C1 to C20 alkylcarboxyl radical, a mono-substituted, di-substituted, or tri-substituted glycerol residue, hydrogen, or combinations thereof; where R3 is hydrogen, a methyl radical, or combinations thereof; where R4 is hydrogen, a branched or straight chain C1 to C20 alkyl radical, a phenyl radical, a C1 to C8 branched or straight chain alkyl-substituted-phenyl radical, a C1 to C20 branched or straight chain acyl radical, or combinations thereof; and where q is 1 to 300.
Lubricating compositions including the reaction products and adducts of the present invention are also provided. Advantageously, the lubricating compositions of the present invention exhibit significantly improved Timken loads as compared previous DMTD derivatives. These and other advantages of the present invention will be readily apparent from the detailed description set forth below.
Present invention provides reaction products and adducts of substituted-2,5-dimercapto-1,3,4-thiadiazole dimers (hereinafter xe2x80x9cthiadiazole dimersxe2x80x9d) and poly(ether)glycols useful as extreme pressure additives in lubricants. The thiadiazole dimer-glycol reaction products and adducts have unexpectedly been found to provide good Timken Load properties in addition to good 4-Ball Weld properties. In addition, the reaction products and adducts are biodegradeble at low concentrations. Advantageously, the reaction products and adducts provide a more environmentally-friendly alternative to the heavy metal extreme pressure additives commonly used in lubricants.
In one embodiment the present invention provides an additive including a reaction product of a thiadiazole dimer and a poly(ether)glycol. The thiadiazole dimer is a 2,5-dimercapto-1,3,4-thiadiazole (DMTD) monsulfide or disulfide dimer having formula (I): 
in which xe2x80x9cnxe2x80x9d is 1 to 2 and the substituent xe2x80x9cZxe2x80x9d is either: (1) hydrogen; (2) an alkyloxy linkage having formula (II): 
or combinations thereof. When Z is an alkyloxy linkage, xe2x80x9ctxe2x80x9d is 0 or 1 and the substituent R1 is either: (1) hydrogen; (2) a branched or straight chain C1 to C7 alkyl radical, with a C1 to C4 alkyl radical being preferred; or a combination thereof. Likewise, the substituents for R2 are independently chosen from the same group of substituents described for R1. In a preferred embodiment, when Z is an alkyloxy linkage xe2x80x9ctxe2x80x9d is 0, R1 is an ethyl radical and R2 is a propyl radical.
Thiadiazole dimers falling within the above-described parameter are known in the art and are easily synthesized following known techniques. For example, the DMTD disulfide dimer (5,5xe2x80x2-dithiobis(1,3,4-thiadizole-2-thiol) is disclosed in U.S. Pat. Nos. 4,517,103 and 3,161,575, which are incorporated herein by reference. The DMTD disulfide dimer is also commercially available under the trade name VANLUBE(copyright)829 from R.T. Vanderbilt, Company, Inc. The DMTD monosulfide dimer (5,5xe2x80x2-thiobis (1,3,4-thiadiazole-2-thiol) is also commercially under the tradename VANAX(copyright)882A from R.T. Vanderbilt, Company, Inc. The thiadiazole dimers having the alkyloxy linkage of formula (II) with xe2x80x9ctxe2x80x9d being zero (0) are disclosed in U.S. Patent No. 5,194,621, which is incorporated herein by reference.
The second component for synthesizing the thiadiazole dimer-glycol reaction product is a poly(ether)glycol having formula (III): 
in which F is either: (1) a hydroxyl radical; (2) a branched or straight chain C1 to C20 alkoxyl radical, with a C1 to C0 radical being preferred; (3) a branched or straight chain C1 to C20 alkylcarboxyl radical, with a C1 to C10 radical being preferred; (4) a mono-substituted, di-substituted, or tri-substituted glycerol residue; (5) hydrogen; or a combination thereof. The substituent R3 is either: hydrogen; a methyl radical; or a combination thereof The substituent R4 is either: (1) hydrogen; (2) a branched or straight chain C1 to C20 alkyl radical, with a C1 to C8 radical being preferred; (3) a phenyl radical; (4) a branched or straight chain C1 to C20 alkyl-substituted-phenyl radical, with a C1 to C8 alkyl substituent being preferred; (5) a branched or straight chain C1 to C20 acyl radical, with a C1 to C10, radical being preferred; or a combination thereof. The number of ether repeating units xe2x80x9cqxe2x80x9d ranges from 1 to 300, with 1 to 150 being preferred, with 1 to 10 being more preferred.
Poly(ether)glycols falling within the above described parameters are known in the art. Representative examples of the glycols include, but are not limited to, polyethylene glycol, polypropylene glycol, tetraethylene glycol, ethyloxytriethylene glycol, butoxytriethylene glycol, dimethoxytriethylene glycol, triethyleneglycol di-nonanoate, butoxytriglycol, and triethyleneglycol dimethylether. One particularly preferred glycol is butoxytriethylene glycol. The glycols are commercial available from a variety of sources. Preferably, the glycols have a molecular weight from 340 to 4000, with 340 to 1000 being preferred. The glycols should have a viscosity less than 4000 centistokes at 25xc2x0 C. for ease of handling. Likewise, the glycols should have a minimal effect on the dropping point of greases.
The reaction product is formed by combining the two sole components with or without a solvent and subsequently heating the components, if necessary. Preferably, the thiadiazole dimer is dispersed in the glycol, since the glycol is normally in a liquid state at room temperature. Heating the thiadiazole dimer-glycol reaction mixture is not required when the thiadiazole dimer is in a liquid state at room temperature. However, if the thiadiazole dimer is in a solid state at room temperature, the mixture may be heated (e.g., to at least 100xc2x0 C.) to facilitate formation of the reaction product. The requisite temperature and time needed to facilitate formation of the reaction product is variable and can easily be determined by one skilled in the art. The formation of the liquid reaction product can approximated by observing the dissolution of the solid thiadiazole dimer. The formation of the reaction product can also be confirmed by Infrared Spectroscopy (IR) since shifts in absorption are observed when comparing the IR spectra for the individual components versus the IR spectra for the reaction product. In addition, to obtain a reaction product lighter in color, a small amount of a reducing agent (e.g., sodium meta bisulfite) is added to the reaction mixture.
The thiadiazole dimer and the poly(ether)glycol are preferably reacted in a molar ratio of the starting material of at least 0.2:1, with at least 0.4:1 being more preferred. However, for further improved extreme pressure properties an equimolar or excess of the thiadiazole starting material can be utilized (e.g., a molar ratio of 1:1, 2:1 or greater).
An alternative method for synthesizing the DMTD mono- and disulfide dimer-glycol reaction product is by reacting DMTD in the prescence of the glycol. It has been found that when DMTD is dispersed in the glycol and heated the DMTD mono- and disulfide dimer forms in situ, as well as 2-mercapto-1,3,4-thiadiazole (MTD). The in situ formation of the dimer can be discerned by the contemporaneous formation of hydrogen sulfide (H2S). Accordingly, one skilled in the art would react 2 moles of DMTD for 1 mole of glycol to provide a DMTD dimer-glycol reaction product having a thiadiazole:glycol starting material ratio of 1:1.
While not wishing to be limited by theory, spectroscopic analysis of the above described reaction products indicate that various isomers of the thiadiazole dimer (I) and MTD monomer may be found in the reaction mixture. The presence of these other thiadiazole compounds is attributed to their presence in the thiadiazole starting material and to isomerization during formation of the reaction product. The thiadiazole compounds also complex with the above-described poly(ether)glycols to form reaction products useful as extreme pressure additives. Spectroscopic analysis indicates that the thiadiazole compounds have the following structures: 
Thus, in accordance with the present invention, the additives of the present invention can further include a mixture of reaction products. In a preferred embodiment, the additive contains the reaction product of the thiadiazole dinner having formula (I) with the poly(ether)glycols as the predominate reaction product, with the remainder being any of the reactions products formed by the thiadiazaole compounds of formulas (IA-IF) complexing with the poly(ether) glycols. The iw term xe2x80x9cpredominatexe2x80x9d in this context preferably means at least 50 percent by weight of the total amount of reaction products present in the additive composition. In an alternative embodiment, the present invention provides an additive that includes at least one reaction product formed from any of the thiadiazole compound having formulas (IA) through (IF) and the above-described poly(ether)glycols.
In another embodiment the present invention provides an additive including mono-substituted and di-substituted thiadiazole condensation adducts having formulas (IV) and (V), respectively: 
in which R1, R3 and R4 are independently selected from the above-described group of substituents for the reaction products and n is 1 to 2. The number of repeating ether units xe2x80x9cmxe2x80x9d in the glycol moiety is 1 to 50, with 1 to 10 being preferred, and 1 to 3 being more preferred.
The substituted thiadiazole dimer-glycol adducts are prepared by reacting the DMTD monosulfide or disulfide dimer with an aldehyde containing the substituent R1 and a poly(ether) glycol falling within the previously described parameters. The components are mixed and heated for a sufficient amount of time to form the condensation adduct. The synthesis of similar condensation adducts using monohydric alcohols instead of glycols are disclosed in U.S. Pat. No. 5,194,621, which is incorporated herein by reference. The mono-substituted thiadiazole dimer-glycol adduct is prepared by reacting the above-described components in a 1:1:1 molar ratio. The reaction mixture may also contain the di-substituted thiadiazole-glycol adduct if complete conversion of DMTD dimer does not occur. Incomplete conversion of DMTD dimer is ascertained by observing whether solid DMTD remains in the reaction mixture. As will be apparent to those skilled in the art, the di-substituted thiadiazole dimer-glycol adduct is prepared by reacting the components in a 1:2:2 molar ratio. Likewise, the reaction mixture may also contain mono-substituted thiadiazole dimer adduct. These parameters can be easily modified by one skilled in the art.
In yet another embodiment, the present invention provides an additive including a thiadiazole dimer- glycol reaction product having a DMTD dimer of formula (VI): 
where xe2x80x9cdxe2x80x9d is 1 to 5, with 1 to 3 being more preferred, and Z is hydrogen, an alkyloxy linkage having formula (II) as described above, or a combination thereof DMTD dimers having formula (VI) are easily synthesized using techniques known in the art. The poly(ether)glycol component and ratios of DMTD dimer to poly(ether)glycol are the same as described above. A particular advantage of the DMTD dimer of formula (VI) is increased oil-solubility due to the hydrocarbon bridge.
In accordance with present invention, the thiadiazole reaction products and adducts are incorporated as additives into lubricating compositions in an effective amount to impart adequate extreme pressure properties. In this context, adequate extreme pressure properties is passing a Timken Load of at least 40 pounds, with at least 50 pounds or greater being preferred. As will be apparent with one skilled in the art, the amount of the reaction products and adducts needed to provide adequate extreme pressure properties is variable. The additives can be added in a range from 0.1 to 10 weight percent of the lubricating composition, with at least 1 weight percent being preferred and 2 weight percent being even more preferred.
Lubricating compositions suitable for incorporation of the extreme pressure additives include, but are not limited to, lubricating oils, engine oils and lubricating greases containing a major amount of base oil. A xe2x80x9cmajor amountxe2x80x9d in this context means that greater than 50 weight percent (wt. %) of the composition is base oil. Base oils to be used include, but are not limited to, napthenic, aromatic, paraffinic, mineral, and synthetic oils. Representative synthetic oils include, but are not limited to, polysiloxanes, carboxylic acid esters and polyglycol ethers.
In a preferred embodiment, the lubricating composition is a grease which is prepared by adding to a base oil thickeners such as salts and complexes of fatty acid soaps, polyurea compounds, mixed and complex soaps of alkali metals, alkaline earth metals, aluminum, modified clays and quatemary ammonium bentonite complexes. Various other additives be incorporated as desired.
The following non-limiting examples illustrate the synthesis of the thiadiazole dimer-glycol reaction products and adducts, and their use as extreme pressure additives in lubricating compositions.